Just played a game as Morgana

Hi, I'm quite new to LoL (level 10). Just played a blind game as Morgana, went bot lane. About a quarter of the way in I decided to switch to mid as I could see a red cluster on the radar there. Player in mid told me to go defend my own lane. I didn't see the message as I was so busy concentrating on wave clearing/enemy attention. They then started accusing me of trolling (again, took me a while to see this) and threatened to go AFK if I didn't leave the lane. When I read it, I explained that I'm not a troll, I'm new, but in the end the player with the issue quit half way through. Obviously I've made a mistake in gameplay, and not reading messages. I'm not sure when to switch lanes to support and when to stay and defend. Is this entirely role dependent?
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